Method and means for operating a blast furnace



Oct. 20, 1964 R. E. TOUZALIN 3,153,532

METHOD AND MEANS FOR OPERATING A BLAST FURNACE Filed Aug. 11, 1960 4 Sheets-Sheet 1 INVENTOR. Roaza'r E. Touzm-m Tune 1' nTToRNEYS 1964 R. E. TOUZALILNZ METHOD AND MEANS FOR OPERATING A BLAST FURNACE Filed Aug. 11, 1960 4 Sheets-Sheet 2 0 o o o o w o 4 w 7 a 9 TIME- HOURS Oct. 20, 1964 R. E. TOUZALlN METHOD AND MEANS FOR OPERATING A BLAST FURNACE 4 Sheets-Sheet 5 Filed Aug. 11, 1960 m T mr m w V TIE .m #M m an u T o !R i Oct. 20, 1964 R. E. TOUZALIN METHOD AND MEANS FOR OPERATING A BLAST FURNACE Filed Aug. 11, 1960 TO STOVE FILLING BLAST PRESSURE CONTROL 55 4 Sheets-Sheet 4 STOVE BURNER CONTROL T I la TO STOVE TO STOVE TO HOT BLAST CONTROL CONTROL TEMPERATURE CONTROL electrical fluid 4 INVENTOR.

ROBERT E. Touznu'u HTTORNEYS United States Patent Q 3,153,532 METHOD AND MEANS FOR OPERATENG A BLAST FURNACE Robert E. Touzalin, Aurora, Uhio, assignor to lnterlake Iron Corporation, Cleveland, Ohio, a corporation of New York Filed Aug. 11, 1960, Ser. No. 49,055 16 Cl. (Cl. 2623-49) This invention relates to the operation of furnaces and more particularly to the operation of vertical shaft furnaces of the blast furnace type used in the manufacture of iron.

In present blast furnace practice, materials consisting of ore, coke and limestone are charged at the top of the furnace and a hot blast of air is blown in near the bottom of the hearth through a number of tuyeres. The hot blast is generally heated to approximately 1000 F. to 1400 F., average temperatures above 1400" being the exception. Heated air for the hot blast is ordinarily obtained from a battery of heating stoves associated with eachv blast furnace. In ordinary operation, the hot air from one or more of these heating stoves is mixed with a cold blast in such proportions as to give the desired temperature of the air blast fed to the blast furnace. When a predetermined amount of heat has been drawn from one of the heating stoves, it is cut off from the conduit leading to the blast furnace and a fresh stove substituted therefor. Conventional practice has been to place a stove on blast when the air temperature in the top or dome of the stove is approximately 2000 F., and then the heated air is drawn from such stove and forced into the blast furnace with the aforementioned predetermined quantity of cold air, until the temperature of the air coming from the stove drops to approximately 100 degrees above the blast temperature, at which time such stove is takenoff blast and another stove which is at the aforementioned 2000 F. top temperature is placed on blast. The stove taken off blast is then reheated back up to its original dome temperature, of for instance 2000 F.

It has also been known in the past to use two stoves in straight parallel, instead of only one stove, and with cold bypass air providing the means for controlling the hot-blast temperature. This is known as unstaggered parallel operation.

-If the blast temperature can be increased from the conventional 1000-1400 F. say, for instance, up to 1700-1800 F., considerable savings in fuel or coke may be accomplished due to the reduced use of the coke in the charge for heating the blast up to the hearth temperature in the furnace of approximately 2800 F. or higher. Moreover, such a higher blast temperature makes it possible to take advantage of certain desirable blast furnace operating techniques, for instance the use of moisture in the blast, and the utilization of natural gas as an auxiliary fuel in the furnace. However, with conventional stove equipment as generally found in existing blast furnace arrangements, the addition of new stoves to the blast furnace or the complete reconstruction of the old stoves would usually be necessitated in order to be able to operate in the aforementioned manner with a fblast temperature of much over 1000l400 F., since as aforementioned, such equipment has been generally designed to operate the blast at approximately 1000- 1400 F. with the aforedescribed conventional practice in stove operation.

The present invention provides a method of operation of the stoves of a blast furnace arrangement so that the blast temperature can be increased and maintained above the aforementioned conventional 1000-1400 F., for

Patented Oct. 20, 1964 instance at 1700-1800 F. or more, thereby increasing the efficiency of the furnace and without the necessity of adding new stove equipment to the furnace or completely rebuilding the old stoves, in order to' obtain the desired increase in blast temperature.

Accordingly an object of the invention is to provide an improved method of operating the stoves of the blast furnace arrangement, to increase the eiiiciency of the furnace.

Another object of the invention is to provide a method which will permit operation of the furnace at a blast temperature of approximately 17001800 F. or more, resulting in a considerable saving of coke in the furnace operation. a

A further object of the invention is to provide a method which permits operation of the blast furnace at a blast temperature considerably above 1300" F., and without the need of adding additional stove equipment to the blast furnace arrangement to obtain and maintain such increased blast temperature.

A still further object of the invention is to provide a system including automatic control means for operating in a predetermined manner the stoves of a blast furnace arrangement, to increase the efiiciency of the furnace.

Other objects and advantages of the invention Will be apparent from the following description taken in conjunction with the accompanying drawings wherein:

FIG. 1 is a diagrammatic showing of a blast furnace equipped with a series of stoves for heating the blast air to the desired temperature.

FIG. 2 is a graph showing in diagrammatic form the correlation between placing a stove on blast and taking a stove off blast in accordance with the method of the invention. I

FIG. 3 is a schematic illustration of an automatic control system for operating the stoves of the blast furnace arrangement in accordance with the invention.

FIG. 4 is an enlarged schematic illustration of one of the stoves of FIG. 3 with the associated system for automatically controlling the operation of the stove.

Referring now again to the drawings, there is shown a typical blast furnace installation comprising a furnace 10, a plurality of stoves 12, 12a, 12b and 120, a blower 14 and cold and hot blast pipes 16 and 18, respectively. Pipes 15 and 18 are connected by the usual cold air bypass line 16a. The furnace may have the usual bustle pipe 20 and tuyeres 22 associated therewith. In accordance with usual practice, air is drawn through an intake 21, and blast flow measuring element 21a, into tl e blower 14. Check valves 21b and snort valve 210 may be provided in the blower discharge line, and in the conventional manner. The blower 14 directs cold air through the cold blast line into the stoves and thence through the hot blast line, bustle pipe and tuyeres, and then into the lower portion of the furnace. The temperature of the blast entering the furnace in conventional practice is generally about 10001400 F., maintained at such temperature by mixing a suitable quantity of cold air via bypass line 16a with the hot air in blast line 18.

Adjustable valves 24, 24a may be mounted in bypass line 16a and cold blast line 16 respectively, together with drop valve 24b in bypass line 16a, to permit cold air from the blower 14 to bypass the stoves via line 16a and thence into hot blast line 18, thereby providing for adjustment of the temperature of the blast at bustle pipe 20 in the heretofore conventional operation of the stoves.

Conventional practice has been to heat thestoves up to an operating temperature of approximately 2000 F. dome temperature by applying fuel thereto such as blast furnace gas, coke-oven gas or natural gas and via the respective feed line 28 for each stove, such supplying of heating fuel being controlled by means of a shut-off valve mechanism 30 and a regulating valve 54 associated with each feed line 28. When the dome temperature of the respective stoves rose to the aforementioned 2000 F, the cold blast valve 32a and hot blast valve 32 associated with each stove were selectively opened thereby connecting the stove with the hot blast line 18. Hot air from the stove on blast was then forced into the hot blast line 13 and fed via the latter to the furnace tuyeres while the valves 24, 24:: were actuated to maintain the 1000-l400 temperature of the blast at the furnace. When the temperature of the stove on blast dropped to approximately 100 F. above the blast temperature such stove was taken oif blast by closing the cold blast valve 32a and hot blast valve 32, and the next stove which had meanwhile been maintained or brought up to the aforementioned 2000 F. dome temperature was simultaneously placed on blast. Meanwhile the exhausted stove which had been taken off blast was fed fuel and was therefore in the process of being brought up to the aforementioned dome temperature of 2000 F.

In the method of producing an increased blast temperature of the present invention, the stoves are preferably heated up to a predetermined temperature, for instance 2100 F. dome temperature, and the heat from the stove on blast, for instance stove E2, is forced into the hot blast line 18, and only during the initial firing of the furnace is mixed with a suitable and predetermined amount of cold air by means of mixer valves 24, 24a until the dome temperature of the stove drops to approximately 1850 P. Then instead of closing the cold blast valve 32a and hot blast valve 32 of the stove, the stove 12 is maintained on blast and another stove, for instance stove 12a is also placed on blast in parallel relation with the first stove 12, in order to provide and maintain the desired 1700 1800 F. blast temperature at the tuyeres. No cold air is mixed with the heated air coming from stoves 12, 12a as in conventional practice, except for an emergency condition, and the temperature of the air in the hot blast line 18 is maintained at the desired blast temperature of approximately 1700-1800 F. by proper and combined adjustment of the temperature regulating valves 33, 33a of stoves 12 and 12a, respectively. Then when stove 12 has finally dropped down to approximately 1700 F., and the stove is removed from blast by closing the cold blast valve 32a and hot blast valve 32 the fuel valve 30 in its feed line 28 is turned on to commence heating stove 12 once again up to the desired operating temperature. Just before stove 12 is taken off blast, stove 12b is placed on blast in parallel with stove 12a which is still on blast. It will be seen therefore that two stoves operating in parallel are on blast at all times, once the firing of the furnace has commenced beyond the partial utilization of the first stove. The temperature regulating valves 33a and 33b of stoves 12a and 12b respectively on blast are adjusted in combination to maintain the desired blast temperature in the hot blast line 18, and no cold air is utilized for controlling the blast temperature, except in an emergency condition.

The larger combined heating surface of two stoves results in a smaller heat transfer rate per unit area of heating surface and therefore a closer approach of the outlet air temperature to brick surface temperature in the stoves, for a given operating rate. Moreover the use of air from a hot stove to supply the heat intensity needed to supplement the heat in the cooler stove, allows the operator to maintain a stove in operation long after its temperature has dropped below the minimum temperature at which it could operate under the conventional practice of aforementioned normal single or unstaggered parallel operation.

A generally accepted theory, backed up by extensive operating data, indicates that an increase in hot blast temperature of 100 F. results in a fuel saving of 25 pounds of coke per ton of pig iron produced. Thus, in a blast furnace producing 2000 tons of pig iron per day, an increase of 300 F. in blast temperature might result in a coke saving of about 75 tons per day. If the cost of coke were $20.00 per ton, the savings realized would be $1500.00 per day or over $500,000.00 per year.

Referring now to FIG. 2 of the drawings, this staggered parallel operation of the group of stoves 12-120 is graphically illustrated. As can be seen, stove 12, initially at approximately 2100 F. dome temperature is placed on blast, and heated air is drawn from the stove until the stoves dome temperature drops to approximately 1850" R, such heated air in combination with cold air through bypass line 1611, providing for a blast temperature of approximately 1700-1800 F. at the tuyeres, as aforedescribed. When stove 12 reaches a dome temperature of approximately 1850 F., stove 12a is placed on blast in parallel with stove l2, and the temperature regulating valves 33, 33a of the respective stoves are adjusted in unison to maintain the desired blast temperature of 1700- 1800 F. without any cold air. When stove 12 reaches a dome temperature of approximately 1700 B, it is taken off blast and placed on gas to be heated back up and stove 12b is placed on blast in parallel with stove 12a, and valves 33a and 33b of stoves 12a and 12b are adjusted to maintain the desired blast temperature. Then when stove 1.2a drops to approximately 1700 F. dome temperature, stove 12a is taken off blast and stove 12c substituted therefor in parallel with stove 12b. Stove 12b is then operated in conjunction with stove until the temperature of stove 12b drops to approximately 1700 F., at which time stove 12b is taken off blast and placed on gas and stove 12 which has been heated back up to operating temperature is placed on blast with stove 120. The cycle is then continuously repeated with at least two stoves being in parallel operation on blast at all times.

Referring now to FIG. 3, there is schematically illustrated a system for automatically controlling the aforedescribed operation of the stoves, with FIG. 4 being an enlarged view of each stove and its associated operating components of the system. A temperature measuring element such as a thermo-couple 40 is connected into the hot blast line 18 to indicate the temperature of the blast entering the furnace. The temperature measuring element 40 is attached to an automatic hot blast temperature control 42 which in turn is connected via line 43 to aforementioned valves 24, 24a, and via lines 43a, 43b, 43c and 43d to the aforementioned temperature regulating valves 33, 33a, 33b and 33c of the respective stove, to maintain the blast temperature at the furnace at the desired value.

The hot blast temperature control 42 is connected via electrical signal line 44 to the stove control 45, the latter being operated by the furnace operator. Thus the hot blast temperature control 42 following the instructions of the stove control 45, modulates the temperature regulating valves (i.e. 33, 33a, 33b, 330) at either or both the hot or cold stoves which are on blast, to mix the air blast from the two stoves in such proportion that the desired pre-set hot blast temperature (for instance 1700- 1800 F.) is maintained throughout the operating sequence. When the heat in the cold stove is nearly depleted, as indicated, for example, by the position of the cold stove regulating valve, a signal is transmitted via hot blast temperature control 42 to the stove control 45 and a stove change is initiated by the latter. If the temperature regulation outlined above is not effective in limiting the blast temperature below the pre-set maximum, the valves 24, 24a automatically become operative and cold air is bypassed around the stoves through the emergency mixer line 16a. I

The stove control 45 interconnects and coordinates all of the heretofore and hereafter mentioned individual controls for the various operating elements of the stoves, and by changing the stove control settings, control of all stove operating functions is possible. Such stove control may automatically sequence valve operations to actuate hot blast valve 32, cold blast valve 32a and relief valve 90 of the respective stove via electrical signal line 47, to place the stove on blast or to take the stove oif blast. Such stove control 45 may also automatically actuate via line 47 the burner 46' and associated air blower 46" associated with each stove, and thus place the stove on gas and take the stove off gas. Each stove also has an automatic stove burner control 46 associated therewith, which burner controls of all the stoves are coordinated by the stove control 45 to assure proper operation of each burner in correct sequence with the other stove operations. The stove control 45 also activates a stove filling blast pressure control 58 (to be hereinafter described) in proper sequence with stove changing operations.

The stove burner control 46 at each stove is connected to the stove control 45 via line 49 and is preferably designed to burn gas with enough excess air to limit the flame temperature Within desired levels. Air-gas ratio is regulated by position of valve 48 (FIG. 4) in the air duct to the burner. Flow meters in both the air main and the gas main 5% provide measurement of air and gas flow. A thermocouple 52 in the breaching at each stove adjacent the chimney valve 52a provides a measurement of stove stack temperature. When this temperature exceeds a pre-set control point, gas flow is reduced automatically by a control valve 54 which throttles the gas How to the burner. Each stove is preferably also provided with a dome thermocouple 56 which provides an auxiliary safety device for actuating the stoves burner control, thereby insuring against any overrun of the maximum safe limit of dome temperature of the stove.

The aforementioned stove filling blast pressure control 58 is connected via pressure impulse line as (FIG. 3) with a pressure sensitive element 62 connected into the hot blast line 18 at the bustle pipe 2% to measure the pressure of the blast entering the furnace. Control 58 is connected via electrical signal line 62a to stove control 45. Immediately prior to the start of stove filling, a measurement of cold blast line pressure is taken, as at 64, and via impulse line 60a, and retained as a set point for pressure control during the filling operation. When a stove going on blast is to be brought up to cold blast line pressure, a signal from the stove control 45 to the blower control 66 causes the blower to increase air delivery rate. As the blower delivers more air than is being used by the blast furnace, the excess air is used for air filling the selected stove. As the air flow from the blower exceeds the normal blowing rate, the blast pressure control 58, via electrical signal lines 67, partially opensthe filling regulating valve 68 of the respective stove, the filling valve 70 in filling line 72 having been opened by a signal from control panel 45 via electrical line 74. Control 58 modulates the position of valve 68 to maintaina constant cold blast main pressure in'accordance with the aforementioned pressure set point. To correct for a change in rate of air flow through the stoves, any'change in pressure drop through the stoves results in an automatic adjustment of the pressure set point. If the stove filling progresses at too slow a rate, a command from the stove control 45 overrides the pressure control 58 and opens the filling regulating valve 68 far enough to maintain a prescribed filling rate. This slow rate condition is detected by the differential pressure transmitter 76 associated with each stove and connected to the cold blast line 16 and to the stove intake line 73 of the respective stove by pressure impulse lines 80. The pressure transmitter 76 is connected via electrical signal line 82 to stove control 45. The pressure control 58 sends an emergency signal to the stove control45 when the cold blast. line pressure cannot be controlled within desired limits. Thus in case the stove filling line 72 cannot accommodate the entire excess air delivery of the blower, the stove control provides a signal to the blower 6 control 66 to slowdown the blower to an air delivery rate which can be handled at the stove being filled.

It will be understood that the controls for controlling the individual stoves in the method of the invention involving maintaining two stoves, a cold stove and a hot stove, in parallel operation on blast at all times and selectively withdrawing heated air from the stoves to maintain a predetermined relatively high hot blast temperature without the addition of unheated air, could be operated manually at the individual controls but an automatic system is preferable.

Aforementioned stove control 45 may be obtained from the Leeds and Northrup Company of Philadelphia, Pennsylvania, producing a control identified as No. CLE-60- 584, or the Koppers Company of Pittsburgh 19, Pennsylvania, producing an automatic stove control known as The FreynDesign Automatic Stove Changing Con trol System identified by Koppers Pamphlet MOF94 59. Hot blast temperature control 42 may likewise be obtained from the Leeds and Northrup Company producing a control known as the Model S Speedomax Type G Recorder and Controller and described in Leeds and Northrup Company Catalog ND46 (1)-l952. Stove Burner Control 46 may be obtained from the B-I-F In dustries Inc. of Providence, Rhode Island and is described and shown in their brochure entitled Hot Blast Stove Control which includes their drawing No. D- 590209 dated February 9, 1959. Pressure Control 58 may be obtained from the Askania Regulator Company of Chicago, Illinois and is identified by their drawing No. LF-55-7767-IG dated September 20, 1955. The blower control 66 may likewise be obtained from the Askania Regulator Company and is shown on their drawing No. LC-56-3968-l dated December 4, 1956 and described in their Technical Paper No. 205 dated March 1950 and entitled Turbo-Blower Control.

From the foregoing description and accompanying drawings it will be seen that the invention provides a method and associated control system for operating stoves of a blast furnace arrangement in staggered-parallel relation, to permit operation of the blast furnace at a blast temperature of Well'above the conventional l0O0l400 F., 'resulting in a considerable increase in the efiiciency of a furnace and a considerable saving of coke in the furnace operation, and without the necessity of adding new stoves or completely reconstructing the old stoves of existing furnace installations.

The terms and expressions which have been used are used as terms of description and not of limitation and there is no intention in the use of such terms and expressions of excluding any equivalents of any of the features shown or described, or portions thereof, but it is recognized that various modifications are possible Within the scope of the invention claimed.

I claim:

1'. In the operation of a blast furnace wherein the ho air blast for the furnace is heated to a predetermined temperature above 1000-1400 F. by a plurality of blast furnace stoves, the method of producing and maintaining said predetermined blast temperature comprising, placing one of the stoves. which has been heated to a dome temperature higher than said predetermined blast temperature on blast and withdrawing heated air from said one stove into the hot blast line until the temperature of air from said one stove drops to approximately the value of said predetermined blast temperature, placing another stove on blast in parallel operating relation to said one stove which other stove has been previously heated to a dometemperature greater than said predetermined blast temperature and withdrawing heated air simultaneously, in a selective manner from both stoves into the blast line to'maintain said predetermined blast temperature, and then continuing to withdraw heated air simultaneously from both of said stoves in a selective manner, by adjustment of the amount of heated air being withdrawn from each stove of the pair on blast, to maintain said predetermined blast temperature without the introduction of unheated air.

2. In the operation of a blast furnace wherem the hot air blast for the furnace is heated to a predetermined temperature above 1000-1400 F. by a plurality of blast furnace stoves, the method of producing and maintaining said predetermined blast temperature comprising the steps of, heating one of the stoves to a dome temperature of a greater value than said predetermined blast temperature, placing said one stove on blast and wlthdrawmg heated air from said one stove into the hot blast line until the temperature of air from said one stove drops to approximately the value of said predetermined blast temperature, placing another stove on blast in parallel operating relation to said one stove which other stove has been previously heated to said stove dome temperature and withdrawing heated air simultaneously, in a selective manner from both stoves into the hot blast line to maintain said predetermined blast temperature, and then continuing to withdraw heated air simultaneously from both of said stoves in a selective manner, by adjustment of the amount of heated air being withdrawn from each stove of the pair on blast, to maintain said predetermined blast temperature without the introduction of unheated air.

3. In the operation of a blast furnace wherein the hot air blast for the furnace is heated to a predetermined temperature above 1000-l400 F. .by a plurality of blast furnace stoves, the method of producing and maintaining said predetermined blast temperature comprising the steps of heating one of the stoves to a predetermined dome temperature above said predetermined blast temperature, placing said one stove on blast and withdrawing heated air from said one stove into the hot blast line until the temperature of air from said one stove drops to approximate ly the value of said predetermined blast temperature, placing another stove on blast in parallel operating relation with said one stove, which other stove has been previously heated to said stove dome temperature and withdrawing heated air simultaneously, in a selective manner from both stoves into the hot blast line to maintain said predetermined blast temperature, continuing to Withdraw heated air simultaneously from both of said stoves in a selective manner, by adjustment of the amount of heated air being withdrawn from each stove of the pair on blast, to maintain said predetermined blast temperature without the introduction of unheated air and until the temperature in said one stove drops to a predetermined minimum value, taking said one stove ofi blast and simultaneously placing another hot stove on blast in parallel operating relation with the second stove, and withdrawing the heated air simultaneously in a selective manner from the second and third mentioned stoves into the hot blast line, to maintain said predetermined blast temperature, and then continuing to withdraw heated air simultaneously from both said second and third mentioned stoves in a selective manner, by continual adjustment of the amount of heated air being withdrawn from each of the stoves on blast, to maintain said predetermined blast temperature without the introduction of unheated air.

4. In the operation of a blast furnace wherein the hot air blast for the furnace is heated to a predetermined tem perature of approximately 1700-1800 F. or higher by a plurality of blast furnace stoves, the method of producing and maintaining said temperature comprising the steps of, heating a first one of the stoves to a dome temperature above said blast temperature, heating other of the stoves to dome temperatures of approximately 2100 F., placing said first stove on blast and withdrawing heated air from said first stove into the hot blast line until the temperature of air from said first stove drops to approximately the value of said predetermined blast temperature, placing one of said other stoves on blast in parallel operating relation with the first stove, and withdrawing heated air simultaneously in a selective manner from both stoves into the hot blast line to maintain said predetermined blast temperature, continuing the withdrawal of heated air simultaneously from said both stoves on blast in a selective manner, by continual adjustment of the amount of heated air being withdrawn from each stove of the pair on blast, to maintain said predetermined blast temperature without the introduction of unheated air, and until the temperature of said first stove drops to a predetermined minimum value, taking said first stove off blast and simultaneously placing a further one of said stoves on blast in parallel operating relation with said one of said other stoves, and withdrawing heated air simultaneously, in a selective manner from said one of said other stoves and said further one of said other stoves into the hot blast line to maintain said predetermined blast temperature, and then continuing the withdrawal of heated air simultaneously from said one of said other stoves and said further one of said other stoves into the hot blast line in a selective manner, by continual adjustment of the amount of heated air being withdrawn from each stove of the pair on blast, to maintain a predetermined blast temperature without the introduction into the blast of unheated air.

5. In the operation of a blast furnace including a plurality of blast furnace heating stoves wherein the hot air blast for the furnace is maintained at a temperature of approximately 17001800 F. at its entry into the furnace, the method of providing and maintaining said blast temperature comprising the steps of, heating a first one of the stoves to a dome temperature of approximately 2100 F., while heating other of the stoves to dome temperatures of approximately 2100 F., placing said first stove on blast and withdrawing heated air from said first stove into the hot blast line while mixing colder air with the withdrawn air from the first stove to maintain said predetermined blast temperature, until the dome temperature in said first stove drops to approximately 1850 F., placing a selected one of said other stoves on blast in parallel operating relation with said first stove, and withdrawing heated air simultaneously, in a selective manner from both stoves into the hot blast line to maintain said predetermined blast temperature without the introduction of unheated air, continuing the withdrawal of heated air simultaneously from both stoves on blast in a selective manner, by continual adjustment of the amount of heated air being withdrawn from each stove of the pair on blast, to maintain said predetermined blast temperature without the introduction of unheated air, until the dome temperature in said first stovedrops to approximately 1700 F., taking said first stove off of blast and simultaneously placing a further one of said other stoves on blast in parallel operating conjunction with said one of said other stoves, and withdrawing heated air simultaneously in a selective manner from said one and said further one of said other stoves into the hot blast line to maintain said predetermined blast temperature, without the introduction of unheated air, continuing the withdrawal of heated air simultaneously from both stoves on blast in a selective manner, by continual adjustment of the amount of heated air being withdrawn from each stove of the pair on blast, to maintain said predetermined blast temperature without the introduction of unheated air, and heating said first stove back up to said dome temperature of 2100 F.

6. In a blast furnace arrangement including a plurality of heating stoves and hot and cold blast lines between which are disposed in parallel operating communicable relation the stoves for heating the hot air blast for the furnace to a predetermined temperature above 1000- 1400 F. and including valve means associated with the blast air inlet and the blast air outlet of each of the stoves for selectively placing the stoves on blast and taking the stoves off blast, and gas control means associated with each of the stoves for selectively placing the stoves on gas and taking the stoves off gas, the combination therewith of other valve means associated with each of the stoves for selectively varying the exodus of heated air from the respective stove into the hot blast line when the stove is on blast, a temperature measuring means adjacent the entry point of the hot air blast into the furnace, and temperature control means coacting between said other valve means and said temperature measuring means for automatically correlating the movement of said other valve means of a pair of said stoves including a hot stove and a colder stove when the latter are disposed on blast in parallel operating relation, so as to maintain said predetermined blast temperature.

7. In a blast furnace arrangement in accordance with claims 6, including a bypass line extending between the cold blast line and the hot blast line for bypassing cold air into the hot blast line, valve means in said cold blast line and said bypass line for selectively controlling entry of cold air into said hot blast line, said temperature control means controlling the operation of said last mentioned valve means whereby said valve means in said bypass line is normally disposed in closed condition, but is movable to a predetermined open position by said temperature control means if the temperature measuring means signals that the first mentioned valve means of said stoves on blast are inadequate to maintain said predetermined blast temperature.

8. In a blast furnace arrangement comprising a plurality of heating stoves and hot and cold blast lines between which' are disposed in parallel operating, communicable relation the stoves for heating the hot air blast for the furnace to a predetermined blast temperature above 1000-1400 F. and including stove changing means comprising means associated with each of the stoves for selectively placing the stoves on blast and taking the stoves off blast and means associated with each of the stoves for selectively placing the stoves on gas and taking the stoves off gas, the combination therewith of valve mean associated with each of the stoves for selectively varying the exodus of hot air from the respective stove into the hot blast line when the stove is on blast, temperature measuring means adjacent the entry point of the hot air blast into the furnace, and temperature control means coacting between said valve means and said temperature measuring means for automatically modulating said valve means of a pair of said stoves including a hot stove and a colder stove which are on blast in parallel operating relation, so as to mix the air blast from said pair of stoves in such proportion thatthe desired predetermined hot blast temperature is maintained, and stove control means coacting between said stove changing means and said temperature control means for automatically initiating a stove change of a hot stove for the colder stove in said paired arrangement, to maintain said blast temperature at said predetermined value upon ya signal furnished by said temperature control means.

9. A system for automatically controlling the opera tion of a blast furnace comprising, a plurality of blast furnace heating stoves, cold and hot blast lines between which said stoves are disposed in parallel operating communicable, relation, a blower communicating with said lines, and wherein the hot air blast for the furnace is adapted to be heated to 'a predetermined temperature above lOO-1400 F., stove changing means coacting with each of the stoves for placing a respective stove on blast, taking a respective stove off blast, placing a respective stove on gas, and taking a respective stove off gas, valve means coacting with each of the stoves on the intake side thereof for selectively varying the exodus of heated air from the respective stove into the hot blast line, temperature measuring means adjacent the entry point of the hot blast line into the furnace, temperature control means coacting between said temperature measuring means and said valve means for automatically modulating said valve means of a pair of stoves, including a hot stove and a relatively colder stove, disposed in parallel operating relation 'on blast, so as to maintain said pre-" determined blast temperature without the introduction in-- to the blast of unheated air, and stove control means coacting between said temperature control means and said stove changing means for automatically initiating a stove change of substituting a hot stove for the colder stove, when said temperature control means indicates that said paired stove arrangement operating in parallel condition is inadequate to maintain said predetermined blast temperature.

10. In a system for automatically controlling the operation of a blast furnace, comprising, a plurality of blast furnace heating stoves for maintaining the hot air blast for the furnace at a temperature above 1000-1400 F., cold and hot blast lines between which are disposed in parallel operating, communicable, relation said stoves, a blower communicating with said lines, stove changing means coacting with each of said stoves for placing the respective stove on blast, taking the respective stove oif blast, placing the respective stove on gas, and taking the respective stove oif gas, valve means coacting with each of the stoves on the intake side thereof for selectively varying the exodus of heated air from the respective stove into the hot blast line for providing for the mixing of the hot air from a pair of said stoves, including a hot stove and a relatively colder stove on blast in parallel operating relation, and in such proportion so as to maintain said predetermined blast temperature, temperature measuring means adjacent the entry point of the hot blast into the furnace, temperature control means coact ing between said valve means and said temperature measuring means for automatically correlating the movement of said valve means of said paired arrangement of stoves,- so as to maintain said predetermined blast temperature without the introduction into the blast of unheated air, stove control means coacting between said stove changing means and said temperature control means for automatically initiating a stove change of a hot stove for the colder stove in said paired arrangement to maintain said blast temperature at said predetermined value upon a signal furnished by said temperature control means, said stove control means also controlling the rate of delivery of said blower, pressure measuring means disposed adjacent the entry point of said hot blast into the furnace, and a stove filling blast pressure control means operably connected to said pressure measuring means and coacting between said cold blast line and said stove control means for causing the latter to control the blower air delivery rate in a manner to maintain a predetermined constant undiminished blast flow during stove filling.

'11. A system in accordance with claim 9, including means for controlling the rate of delivery of the blower, said stove control means controlling said blower control means, and stove filling blast pressure control means coacting between said cold blast line and said stove con trol means for causing the latter to control the blower air delivery rate to maintain a predetermined constant undiminished blast flow during stove filling.

12. A system in accordance with claim 10 wherein each of said stoves comprises a separate stove filling entry line and control means associated therewith, said stove filling control means being operably connected to said stove control means and to said stove filling blast pressure control means, the predetermined rate of stove filling of the respective stove being normally controlled by said stove filling blast pressure control means unless the filling is progressing at too slowly a rate at which time said stove control means overrides said blast pressure control means to further actuate said stove filling control means and maintain a predetermined filling rate.

13. A system in accordance with claim 10 wherein each of said stoves comprises a separate stove filling entry line and control means associated therewith, said stove filling control means comprising a filling valve operably connected to said stove control means and a filling regulating valve operably connected to said stove filling blast pressure control means, said blast pressure control means maintaining a predetermined constant blast fiow during stove filling of the respective stove by actuation of said filling regulating valve in conjunction with varying of said blower air delivery rate.

14. A system in accordance with claim 12 including a differential pressure transmitter coacting between the cold blast line and said stove filling entry line, said transmitter being operably connected to said stove control means for indicating to the latter the necessity of overriding said blast pressure control means.

15. In the operation of a blast furnace including a blower wherein the furnace utilizes a hot air blast and such hot air blast is heated to a predetermined temperature above l000-1400 F. by a plurality of blast furnace stoves disposed in parallel operating, communicable, relation between a cold blast line and a hot blast line with the cold and hot blast lines communicating with the blower, the method of producing and maintaining said predetermined blast temperature at a predetermined blast pressure at the entry point of said hot air blast into the furnace comprising, providing separate entry of filling air for the respective stoves from the cold blast line as compared to the entry of cold blast air from said cold blast line, heating said stoves to predetermined dome temperatures above said predetermined blast temperature, placing one of the stoves which has been previously filled and heated, on blast and forcing heated air from said one stove into the hot blast line and by forced entry of said cold blast air into said one stove until the temperature of air from said one stove drops to approximately the value of said predetermined blast temperature, placing another stove on blast in parallel operating condition with said one stove which other stove has been previously filled and heated, forcing heated air simultaneously from both of said stoves, by said forced entry of cold blast air into said both of said stoves, and in a selective manner, and continuing such forcing of heated air simultaneously from the pair of stoves on blast in a selective manner, by continual adjustment of the amount of heated air being forced from each stove into the hot blast line, of the pair of stoves on blast, so that the mixture of hot air exiting from the combined stove source is maintained at said predetermined blast temperature without the introduction into the hot blast line of unheated air, until the temperature of said one stove drops to a predetermined minimum value, taking said one stove 01f blast and simultaneously placing another stove on blast in parallel operating rela-' tion with the second mentioned stove, which third mentioned stove has been previously filled and heated, forcing heated air simultaneously in a selective manner from said second and third mentioned stoves, and continuing such forcing of heated air simultaneously from the pair of stoves on blast in a selective manner,by continual adjustment of the amount of heated air being forced from each stove of the pair of stoves on blast, to maintain said predetermined blast temperature without the introduction into the hot blast line of unheated air, measuring the cold blast line pressure to obtain a set point for reference to said predetermined blast pressure during a filling operation on said one stove, stepping up the output of the blower so that the air flow therefrom exceeds the normal blowing rate for the stoves on blast, and opening said air filling entry of said one stove to fill the latter with the excess air coming from the blower to thereby maintain said predetermined blast pressure at said entry point into the furnace during said stove filling operation.

16. In the operation of a blast furnace wherein the hot air blast for the furnace is heated to a predetermined temperature above 10001400 F. by a battery of blast furnace stoves the method of producing and maintaining said predetermined blast temperature comprising, heating the stoves to dome temperatures above said predetermined blast temperature, placing a pair of said stoves in parallel operating relation on blast and wherein one of said pair of stoves is a hot stove at a dome temperature above said predetermined blast temperature and the other of said pair of stoves is a colder stove as compared to said hot stove, and forcing heated air simultaneously from said pair of stoves into a hot blast line for the furnace in a selective manner so that the mixture of heated air exiting from said paired arrangement of stoves is maintained at substantially said predetermined blast temperature, and continuing the forcing of heated air simultaneously from said pair of stoves on blast in a selective manner, by adjustment of the amount of heated air being forced from each stove of the pair on blast, to maintain said predetermined blast temperature without the introduction of unheated air.

References Cited in the file of this patent UNITED STATES PATENTS 1,816,174 Brown July 28, 1931 1,941,446 Isley Dec. 26, 1933 2,601,979 Rice et a1. July 1, 1952 2,931,635 Braun et al. Apr. 5, 1960 3,034,775 Jansen et al. May 15, 1962 FOREIGN PATENTS 900,286 France Sept. 25, 1944 

1. IN THE OPERATION OF A BLAST FURNACEWHEREIN THE HOT AIR BLAST FOR THE FURNACE IS HEATED TO A PREDETERMINED TEMPERATURE ABOVE 1000+1400*F. BY A PLURALITY OF BLAST FURNACE STOVES, THE METHOD OF PRODUCING AND MAINTAINING SAID PREDETERMINED BLAST TERMPERATURE COMPRISING, PLACING ONE OF THE STOVES WHICH HAS BEEN HEATED TO A DOME TEMPERATURE HIGHER THAN SAID PREDTERMINED BLAST TEMPERATURE ON BLAST AND WITHDRAWING HEATED AIR FROM SAID ONE STOVE INTO THE HOT BLAST LINE UNTIL THE TEMPERATURE OF AIR FROM SAID ONE STOVE DROPS TO APPROXIMATELY THE VALUE OF SAID PREDETERMINED BLAST TEMPEATURE, PLACING ANOTHER STOVE ON BLAST IN PARALLEL OPERATING RELATION TO SAID ONE STOVE WHICH OTHER STOVE HAS BEEN PREVIOUSLY HEATED TO A DOME TEMPERATURE GREATER THAN SAID PERDETERMINED BLAST TEMPERATURE AND WITHDRAWING HEATED AIR SIMULTANEOLUSLY, IN A SELECTIVE MANNER FROM BOTH STOVESINTO THE BLAST LINE TO MAINTAIN SAID PREDETERMINED BLAST TEMPERATURE, AND 